A casing thread leak-off simulation device and test method

Abstract

The application provides a casing thread leakage plugging simulation device and a test method, which comprises a male thread joint and a female thread joint arranged in an upper and lower manner and screwed with each other, the structure after screwing is a columnar body with a hollow cavity and closed at both ends, an injection module is detachably and sealingly installed at the top closed end of the columnar body, and a drainage module is detachably and sealingly installed at the bottom closed end of the columnar body; a simulation liquid enters the columnar body from the injection module, and is discharged from the screwed thread part of the columnar body and / or the drainage module. Through simulation of the conditions of temperature, pressure and thread leakage rate in the well, the leakage conditions of the casing thread and the cement sheath and the plugging effect of the plugging agent can be directly reflected, the technical blank of the simulation test of the plugging performance of the casing thread leakage plugging agent is filled, and the blindness of the casing thread leakage plugging construction is avoided.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas exploration and development, and relates to a casing thread plugging simulation device and test method, specifically to a simulation test device and test method for testing the plugging performance of oil and gas well casing thread plugging agent. Background Technology

[0002] As the development of oil and gas reservoirs in major oilfields has largely entered the middle and late stages, due to factors such as the presence of corrosive substances in formation water and well fluids, and internal quality defects in casing threads, casing damage and leakage often occur as the production time of oil, gas and water wells extends, coupled with changes in geological conditions and engineering factors, affecting oil and gas production and development results.

[0003] Casing leakage includes body leakage and thread leakage, with thread leakage being more common. Thread leakage can be categorized into loose threads, misaligned threads, and thread corrosion. For thread leakage, casing thread plugs are commonly used to seal the leakage channels. However, previous methods for evaluating plugging agent performance were overly simplistic, merely testing the compressive and shear strength of the cured block sample, which doesn't directly reflect the actual sealing effect of the downhole casing. In fact, there is a cement sheath outside the casing; if casing leakage occurs, it means the cement sheath has also been damaged. Both the casing and the cement sheath are elastic; due to temperature and pressure changes, the leakage channel will deform under alternating loads. Excessively hard plugs may crack. Therefore, higher hardness after curing is not always better; a combination of sufficient strength and high toughness is required.

[0004] Therefore, whether it's an existing or newly developed plugging agent, its ability to truly seal the casing threads can only be scientifically evaluated through indoor simulation tests to assess its sealing performance. Otherwise, casing thread sealing construction is done blindly. To study the sealing effect of casing thread plugging agents, it is necessary to develop a simulation test device and test method for testing the sealing performance of casing thread plugging agents. Summary of the Invention

[0005] The purpose of this invention is to provide a sleeve thread leak-proof simulation device and test method to overcome the above-mentioned technical defects.

[0006] To solve the above-mentioned technical problems, the present invention provides a sleeve thread plugging simulation device, including a male thread connector and a female thread connector arranged vertically and screwed together. The structure after screwing together is a columnar body with closed ends and a hollow cavity. An injection module is detachably and sealed at the closed top end of the columnar body, and a drainage module is detachably and sealed at the closed bottom end of the columnar body.

[0007] The simulated liquid self-injection module enters the cylindrical body and is discharged back from the screw thread of the cylindrical body and / or discharged by the self-drainage module.

[0008] Furthermore, the male thread connector is a hollow cylindrical structure that is closed at the top and open at the bottom. An installation hole for the injection module to be screwed in is provided at the center of the closed top end, and the outer circumferential surface of the open bottom end has a tapered external thread, which serves as the male thread of the sleeve.

[0009] Furthermore, the female connector is a hollow cylindrical structure with an open top and a closed bottom. An installation hole for the drainage module to be screwed into is provided at the center of the closed bottom end. The inner circumferential surface of the open top end has a conical internal thread, which serves as the female thread of the sleeve.

[0010] The male and female threads of the sleeve constitute a pair of tapered pipe threads.

[0011] Furthermore, the bottom of the inner cavity of the female connector is an inverted conical drainage funnel, and the center of the drainage funnel is an installation hole for screwing in the drainage module. The drainage module includes at least a drain plug that is screwed into the installation hole for sealing. A small sealing ring is provided at the junction of the drain plug and the female connector.

[0012] Furthermore, the sleeve thread sealing simulation device also includes a concentrically fitted pressure vessel seat and a cement ring from the outside to the inside. A columnar body composed of two screw-connected joints sits inside the cement ring, with the top annular surface of the cement ring located at the waist of the male joint and higher than the top end face of the female joint.

[0013] Furthermore, a heat-melting plastic diaphragm is provided between the pressure vessel seat and the cement ring. The plastic diaphragm is a cylindrical body that is closed at the bottom and open at the top, and the top surface of the plastic diaphragm is higher than the top surface of the cement ring.

[0014] The confining pressure vessel base is a cylindrical body that is closed at the bottom and open at the top. The top open end is sealed with a confining pressure vessel cover screwed on. The male and female threaded connectors and the cement ring are sealed in the cavity formed by the confining pressure vessel base and the confining pressure vessel cover.

[0015] An installation hole is provided in the center of the pressure vessel cover for the injection module to be screwed in.

[0016] The injection module includes at least an injection connector that is screwed into the top mounting hole of the male connector or the pressure vessel cover, and an injection line that passes through the injection connector and extends into the inner cavity of the male connector or the pressure vessel cover. A sealing cone ring fitted on the outer wall of the injection line is also provided in the top mounting hole of the male connector or the pressure vessel cover.

[0017] The sealing cone ring is a spindle-shaped structure made of plastic material, located directly below the injection joint. When subjected to axial pressure from the injection joint, the sealing cone ring undergoes tapering deformation to seal the injection line with the injection joint, the injection line with the male threaded joint, or the injection line with the pressure vessel cover.

[0018] This invention also provides a method for simulating leak sealing of bushing threads, which uses a bushing thread leak sealing simulation device. The test method is as follows:

[0019] S1. Construct a leakage channel

[0020] Screw the injection module into the male connector, and simultaneously screw the drainage module into the female connector;

[0021] Assemble the male and female threaded connectors to form the internal components;

[0022] Adjust the threads of the upper and lower connectors to leave a radial gap at the threaded part, forming a leakage channel;

[0023] Clean water is injected into the columnar body through the injection module pump, and the clean water is discharged back from the screw thread of the columnar body.

[0024] Set a pump pressure value based on the driving pressure of the leaking sleeve thread during on-site testing, adjust the axial screwing depth of the thread and the pump pressure until the clean water return rate reaches the preset value, and record the clean water return rate corresponding to different axial screwing depths under the set pump pressure.

[0025] S2. Simulated downhole cement sheath rupture

[0026] Place the plastic diaphragm kit inside the pressure vessel base;

[0027] Remove the injection module and the drainage module;

[0028] Place the assembled male and female connectors into the plastic diaphragm;

[0029] Fill the annular space between the plastic diaphragm and the two joints with casing cement to form a cement sheath;

[0030] After the cement ring has hardened, remove the plastic diaphragm;

[0031] Remove the male and female connectors, install the injection module and drainage module to assemble the internal components;

[0032] Fill the cavity of the internal component with clean water;

[0033] Then place the internal components into the pressure vessel base;

[0034] Pressure is applied to the inner cavity of the internal component, and the pressure is continuously increased until the cement ring ruptures;

[0035] Simulates a ruptured cement sheath outside the downhole casing;

[0036] S3. Thread plugging performance test

[0037] Inject the sleeve thread sealant to be evaluated into the inner cavity of the inner component until the sleeve thread sealant returns from the crack in the cement ring. At this point, remove the inner component, remove the drainage module, and release the sleeve thread sealant. The sleeve thread sealant at the thread mating surfaces of the two joints remains stationary.

[0038] Inject the dissolving agent into the cavity of the internal component to flush away any remaining plugging agent from the bushing threads;

[0039] Remove the drainage module installed at the bottom of the female connector and remove the injection module;

[0040] Then place the internal components into the pressure vessel base;

[0041] Place the confining pressure vessel cover onto the confining pressure vessel base and screw it on. Install the injection module inside the confining pressure vessel cover.

[0042] The entire device is placed in a water bath and heated, and pressure is applied to the entire internal components. The temperature and pressure are kept constant and stabilized according to the downhole temperature and pressure to simulate the downhole conditions when the plugging agent in the crack of the casing thread and cement sheath is cured. After the plugging agent in the casing thread is completely cured, the heating is stopped, the pump pressure is released, and after the temperature drops to room temperature, the injection module is removed.

[0043] Remove the entire apparatus from the water bath and remove the pressure vessel lid;

[0044] The injection module is installed inside the male connector, and pressure is applied to the inner cavity of the internal component through the injection module;

[0045] The sealant that has hardened inside the bushing thread is pressure tested to test the pressure-bearing capacity of the bushing thread sealant and the results are recorded.

[0046] Replace the male and female threaded connectors and the plastic diaphragm, and change the axial screw depth of the two connector threads to set different radial thread clearances, thereby simulating different leakage rates of the bushing threads. Repeat the above steps to test the sealing effect of the bushing thread plugging agent under different leakage rates.

[0047] Furthermore, in S2 simulation, the downhole cement sheath ruptured, and casing cementing cement was filled into the annular space between the plastic diaphragm and the two joints to form a cement sheath. After the cement sheath solidified, the plastic diaphragm was removed, as detailed below:

[0048] Fill the annular space between the plastic diaphragm and the two joints with casing cement. After the cement sheath has solidified, if the internal parts cannot be removed, place the entire device in a heating furnace to heat and burn off the plastic diaphragm. After the entire device has cooled to room temperature, remove the internal parts and clean the plastic residue from the outer wall of the cement sheath and the inner wall of the pressure vessel.

[0049] The beneficial effects of this invention are as follows:

[0050] This invention utilizes the screw-fitted annular surface of male and female threaded connectors to simulate the threaded surface of the bushing. By adjusting the axial screw-in depth of the male and female threads of the bushing, the radial clearance of the bushing thread can be changed, thereby testing the sealing performance of the thread sealant under different leakage rates of the bushing thread.

[0051] Furthermore, this invention allows two screw-connected joints to be seated inside a confining pressure vessel. A plastic diaphragm is fitted inside the confining pressure vessel. Cement is filled into the annular space between the plastic diaphragm and the two joints to generate a cement ring. This can simulate the leakage and sealing performance of the cement ring on the outside of the casing. The plastic diaphragm isolates the cement ring from the confining pressure vessel, generating a removable casing threaded cement ring structure, which can form an independent casing threaded cement ring sealing performance test system.

[0052] To make the above description of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the internal components of a sleeve thread sealing simulation device.

[0054] Figure 2 This is a schematic diagram of a casing thread plugging simulation device for simulating a cracked cement sheath in a well.

[0055] Figure 3 This is a schematic diagram of a casing thread sealing simulation device used in the casing thread sealing performance test.

[0056] Figure 4 This is a schematic diagram of a device that simulates downhole temperature and pressure during the curing of casing thread plugging agent.

[0057] Explanation of reference numerals in the attached figures:

[0058] 1. Injection pipeline; 2. Injection connector; 3. Sealing cone ring; 4. Male thread connector; 5. Male thread of sleeve; 6. Female thread of sleeve; 7. Female thread connector; 8. Small sealing ring; 9. Drain plug; 10. Drainage funnel; 11. Root of female thread; 12. Cement ring; 13. Plastic diaphragm; 14. Pressure vessel seat; 15. Large sealing ring; 16. Pressure vessel cover. Detailed Implementation

[0059] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0060] It should be noted that, in this invention, the upper, lower, left, and right in the figure are regarded as the upper, lower, left, and right of the sleeve thread sealing simulation device described in this specification.

[0061] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0062] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0063] First implementation method:

[0064] This embodiment relates to a sleeve thread sealing simulation device, referring to... Figure 1 It includes a male connector 4 and a female connector 7 that are arranged vertically and screwed together. The structure after screwing together is a columnar body with closed ends and a hollow cavity. An injection module is detachably sealed and installed at the closed end of the top of the columnar body, and a drainage module is detachably sealed and installed at the closed end of the bottom of the columnar body. The simulated liquid enters the columnar body from the injection module and is discharged back from the screw thread of the columnar body and / or discharged from the drainage module.

[0065] The working process of this sleeve thread sealing simulation device is as follows:

[0066] (1) Constructing a leakage channel

[0067] like Figure 1 As shown, the injection module is screwed into the male connector 4, and the drainage module is screwed into the female connector 7. The male connector 4 and the female connector 7 are assembled to form the internal components. The threads of the upper and lower connectors are adjusted to leave a radial gap at the threaded joint, forming a leakage channel. Clean water is pumped into the columnar body through the injection module. The clean water is discharged back from the screwed thread of the columnar body. A pump pressure value is set according to the driving pressure of the sleeve thread leakage during on-site testing. The axial screwing depth of the thread is adjusted until the clean water discharge rate reaches the preset value. The clean water discharge rate corresponding to different axial screwing depths under the set pump pressure is recorded.

[0068] The mechanism is as follows: According to the local friction formula P=0.513559ρQ 2 / (C 2 A 2Let P be the pressure, ρ be the liquid density, C be a constant, A be the cross-sectional area of ​​the leakage channel, and Q be the displacement, which is the leakage rate. Therefore, under a given pressure, the larger the displacement (leakage rate), the larger the leakage channel. For example, at a pump pressure of 5 MPa, the equivalent leakage rate of a 1 mm channel is 4.3 L / min, and the equivalent leakage rate of a 2 mm channel is 17.5 L / min.

[0069] The aforementioned leakage channels are used to simulate the leakage channels of downhole casing threads. The inner diameter of the leakage channels can be adjusted by adjusting the screw depth of the two joint screws, thereby simulating the plugging situation under different leakage channels and evaluating the plugging performance under various leakage channels.

[0070] The water backflow rate is the leakage rate of the bushing thread. By changing the radial clearance (i.e., the axial screw-in depth of the thread) between the two thread mating surfaces of the joints, the sealing performance of the thread plug can be tested under different leakage rates (i.e., different water backflow rates) of the bushing thread.

[0071] Adjust the threads of the upper and lower connectors to leave a radial gap at the threads, i.e., do not tighten them, to ensure that the clean water (blocking agent) can flow out.

[0072] (2) Simulation of downhole cement sheath rupture

[0073] like Figure 2 As shown, a plastic diaphragm 13 is fitted into a confining pressure vessel 14. The injection module and drainage module are removed. The assembled male and female connectors 4 and 7 are placed into the plastic diaphragm 13. Casing cement is filled into the annular space between the plastic diaphragm 13 and the two connectors to form a cement ring 12. After the cement ring 12 has solidified, the plastic diaphragm 13 is removed, and the male and female connectors 4 and 7 are taken out. The injection module and drainage module are installed to form an internal component. The cavity of the internal component is filled with clean water, and then the internal component is placed into the confining pressure vessel 14. Pressure is applied to the inner cavity of the internal component, and the pressure is continuously increased until the cement ring 12 ruptures, simulating the rupture of the cement ring outside the downhole casing.

[0074] In actual operation, if casing leakage occurs, it means that the cement sheath is also damaged. Therefore, it is necessary to simulate cement sheath rupture. In other words, this implementation method can simultaneously simulate the sealing of casing threads and cement sheath cracks by plugging agent under the conditions of casing leakage and cement sheath rupture, which is closer to the real situation of casing thread leakage in downhole.

[0075] (3) Test of sealing performance of sleeve thread plugging agent

[0076] Reference Figure 3Inject the sleeve thread plugging agent to be evaluated into the inner cavity of the inner component until the sleeve thread plugging agent returns from the crack of the cement ring 12. At this time, remove the inner component, remove the drainage module, release the sleeve thread plugging agent, and leave the sleeve thread plugging agent at the thread mating surfaces of the two joints. Inject the plugging agent dissolving liquid into the inner cavity of the inner component to flush out the residual sleeve thread plugging agent. Remove the drainage module and install it at the bottom of the female joint 7. Remove the injection module and then put the inner component into the confining pressure vessel seat 14.

[0077] Reference Figure 4 Place the confining pressure vessel cover 16 onto the confining pressure vessel seat 14 and screw it on. Install the injection module inside the confining pressure vessel cover 16. Place the entire device into the water bath and heat it. Apply pressure to the inner cavity of the internal components. Keep the temperature and pressure stable according to the downhole temperature and pressure to simulate the downhole conditions when the plugging agent in the crack of the casing thread and cement sheath is cured. Stop heating after the plugging agent in the casing thread is completely cured, release the pump pressure, and after it drops to room temperature, remove the injection module, take the entire device out of the water bath, and remove the confining pressure vessel cover 16.

[0078] Reference Figure 3 The injection module is installed inside the male thread connector 4. Pressure is applied to the inner cavity of the internal component through the injection module to test the pressure of the sealant solidified in the bushing thread (i.e., gradually increase the pressure, stabilize the pressure for a period of time, and continue to increase the pressure until the pressure cannot be stabilized. The highest stabilized pressure value is the pressure bearing capacity. The pressure bearing capacity of the sealant must be higher than the pressure bearing capacity of the original bushing). The pressure bearing capacity of the bushing thread sealant is tested and recorded. A set of male thread connector 4, female thread connector 7 and plastic diaphragm 13 are replaced. The axial screw-in depth of the two connector threads is changed to set different radial thread clearances, thereby simulating different bushing thread leakage rates. The above steps are repeated to test the sealing effect of the bushing thread sealant under different leakage rates.

[0079] like Figure 1 As shown, the male thread connector 4 is a hollow cylindrical structure that is closed at the top and open at the bottom. An installation hole for the injection module to be screwed in is provided at the center of the closed end at the top. The outer circumferential surface of the open end at the bottom has a tapered external thread, which serves as the male thread 5 of the sleeve.

[0080] See Figure 1 The female connector 7 is a hollow cylindrical structure with an open top and a closed bottom. An installation hole for the drainage module to be screwed in is provided at the center of the closed bottom end. The inner circumferential surface of the open top end has a conical internal thread, which serves as the sleeve female connector 6.

[0081] When the two connectors are screwed together, the male thread 5 and the female thread 6 of the sleeve form a pair of tapered pipe threads. By adjusting the axial screwing depth, the radial clearance of the threads can be changed, thereby adjusting the leakage rate of the sleeve threads.

[0082] Depend on Figures 1-4 It can be seen that when the two connectors are screwed together, the root of the sleeve female thread 6 is the female thread root 11.

[0083] The bottom of the inner cavity of the female connector 7 is an inverted conical drainage funnel 10. The center of the drainage funnel 10 is an installation hole for screwing in the drainage module. The drainage module includes at least a drain plug 9 that is screwed into the installation hole. A small sealing ring 8 is provided at the junction of the drain plug 9 and the female connector 7.

[0084] If too much sealant remains at the root of the female thread 11, it will block the channel for verifying the sealing performance of the bushing thread and affect the sealing performance verification of the bushing thread sealant. Therefore, a drainage funnel 10 is designed at the bottom of the female thread connector 7 to help the residual sealant at the root of the female thread 11 to flow out.

[0085] The female connector 7 and the drain plug 9 are connected by threads. There is a small sealing ring 8 between the female connector 7 and the drain plug 9. When the drain plug 9 is tightened, the upper and lower parts of the small sealing ring 8 form a seal with the female connector 7 and the drain plug 9 respectively.

[0086] To simulate cement ring rupture, the casing thread sealing simulation device also includes a concentrically fitted confining pressure vessel seat 14 and cement ring 12 from the outside in, such as... Figure 2 , Figure 3 or Figure 4 As shown, a cylindrical body consisting of two screw-on joints sits inside a cement ring 12. The top annular surface of the cement ring 12 is located at the waist of the male threaded joint 4 and is higher than the top end face of the female threaded joint 7 to simulate real downhole conditions.

[0087] The confining pressure vessel 14 serves multiple functions, including forming the cement ring 12, simulating the confining pressure of casing threads and cementing cement rings, and acting as a protective device for threaded cement ring pressure testing.

[0088] A plastic diaphragm 13 that is heated and melted is provided between the pressure vessel seat 14 and the cement ring 12. The plastic diaphragm 13 is a cylindrical body that is closed at the bottom and open at the top, and the top surface of the plastic diaphragm 13 is higher than the top surface of the cement ring 12. The plastic diaphragm 13 is used to isolate the cement ring 12 and the pressure vessel seat 14, thereby generating a removable sleeve threaded cement ring structure, which can form an independent sleeve threaded cement ring sealing test system.

[0089] The confining pressure vessel seat 14 is a cylindrical body that is closed at the bottom and open at the top. The top open end is sealed with a confining pressure vessel cover 16. The male threaded connector 4, the female threaded connector 7, and the cement ring 12 are sealed in the cavity formed by the confining pressure vessel seat 14 and the confining pressure vessel cover 16. The confining pressure vessel seat 14 and the confining pressure vessel cover 16 are connected by threads. There is a large sealing ring 15 below the thread of the confining pressure vessel cover 16, which forms a seal with the confining pressure vessel seat 14 and blocks the threaded channel between the confining pressure vessel seat 14 and the confining pressure vessel cover 16.

[0090] To install the injection module, a mounting hole is provided in the center of the pressure vessel cover 16 for the injection module to be screwed in.

[0091] like Figure 1 As shown, the injection module includes at least an injection connector 2 that is sealed and screwed into the top mounting hole of the male connector 4 or the pressure vessel cover 16, and an injection line 1 that passes through the injection connector 2 and extends into the inner cavity of the male connector 4 or the pressure vessel cover 16. A sealing cone ring 3 that is fitted onto the outer wall of the injection line 1 is also provided in the top mounting hole of the male connector 4 or the pressure vessel cover 16.

[0092] The sealing cone ring 3 is a spindle-shaped structure made of plastic material. It is located directly below the injection joint 2. After being subjected to the axial pressure of the injection joint 2, the sealing cone ring 3 undergoes cone-shaped deformation to seal the injection line 1 and the injection joint 2, the injection line 1 and the male threaded joint 4, or the injection line 1 and the pressure vessel cover 16.

[0093] The injection line 1 passes through the injection joint 2, the sealing cone ring 3, and the male threaded joint 4 (or the pressure vessel cover 16) from top to bottom. The sealing cone ring 3 is made of plastic material and undergoes tapering deformation under the axial pressure of the injection joint 2. The inner side of the sealing cone ring 3 forms a seal with the injection line 1, and the outer side of the sealing cone ring 3 forms a seal with the male threaded joint 4.

[0094] The injection connector 2 and the male thread connector 4 are connected by threads.

[0095] Second implementation method:

[0096] This embodiment relates to a method for simulating a leak-sealing test of a bushing thread, which uses a bushing thread leak-sealing simulation device. The test method is as follows:

[0097] S1. Construct a leakage channel

[0098] Screw the injection module into the male connector 4 and the drainage module into the female connector 7. Assemble the male connector 4 and the female connector 7 to form the internal components. Adjust the threads of the upper and lower connectors to leave a radial gap at the threaded joints, forming a leakage channel. Pump clean water into the cylindrical body through the injection module. The clean water is discharged back from the screw thread of the cylindrical body. Set a pump pressure value according to the driving pressure of the sleeve thread leakage during on-site testing. Adjust the axial screw-in depth of the thread and the pump pressure until the clean water discharge rate reaches the preset value. Record the clean water discharge rate corresponding to different axial screw-in depths under the set pump pressure.

[0099] Specifically as follows:

[0100] S101. As Figure 1 As shown, the injection line 1 passes through the injection connector 2 and the sealing cone ring 3 in sequence. The injection connector 2, together with the sealing cone ring 3 and the injection line 1, is connected to the upper threaded hole of the male thread connector 4. Tighten the injection connector 2 to ensure that the sealing cone ring 3 generates sufficient sealing force with the injection line 1 and the male thread connector 4.

[0101] S102. Reference Figure 1 Place the small sealing ring 8 on the thread root of the drain plug 9, connect the drain plug 9 to the threaded hole at the lower end of the female connector 7, and tighten the drain plug 9 to ensure that the small sealing ring 8 forms a sufficient sealing force on the female connector 7 and the drain plug 9.

[0102] S103. For example Figure 1 As shown, when connecting the male thread 5 and the female thread 6 of the sleeve, it is important to note that the threads of the male thread 5 and the female thread 6 of the sleeve should not be tightened. This ensures that there is a certain radial gap between the male thread 5 and the female thread 6 of the sleeve to form a leakage channel for the sleeve threads.

[0103] S104. The injection pump injects clean water into the cavities of the two joints through the injection pipeline 1. The clean water returns from the upper end of the sleeve female thread 6. The rate of clean water return under a specific pump pressure is recorded (read from the injection pump control panel). The axial screw-in depth of the sleeve male thread 5 and the sleeve female thread 6 is adjusted until the clean water return rate reaches the set value.

[0104] S2. Simulated downhole cement sheath rupture

[0105] The plastic diaphragm 13 is placed inside the confining pressure vessel 14. The injection module and drainage module are removed. The assembled male and female connectors 4 and 7 are placed inside the plastic diaphragm 13. Casing cement is filled into the annular space between the plastic diaphragm 13 and the two connectors to form a cement ring 12. After the cement ring 12 has solidified, the plastic diaphragm 13 is removed. The male and female connectors 4 and 7 are taken out. The injection module and drainage module are installed to form the internal components. The cavity of the internal components is filled with clean water. The internal components are then placed inside the confining pressure vessel 14. Pressure is applied to the inner cavity of the internal components, and the pressure is continuously increased until the cement ring 12 ruptures, simulating the rupture of the cement ring outside the downhole casing.

[0106] Specifically as follows:

[0107] S201. Insert the plastic diaphragm 13 into the inner wall of the pressure vessel seat 14. After adjusting the axial screwing depth of the male sleeve thread 5 and the female sleeve thread 6, remove the injection line 1, injection connector 2, sealing cone ring 3, drain plug 9 and small sealing ring 8.

[0108] S202. Place the male casing thread 5 and the female casing thread 6 into the center of the plastic diaphragm 13 inside the confining pressure vessel 14, and fill the prepared casing cementing cement into the annular space between the male thread connector 4 and the female thread connector 7 and the plastic diaphragm 13.

[0109] S203. After the cement ring has solidified, if the internal parts cannot be removed smoothly, put the entire device into the heating furnace for heating. The high temperature will burn off the plastic diaphragm 13. The temperature should be controlled to be lower than the phase change temperature of the steel, otherwise it will affect the mechanical properties of the device. After the temperature of the entire device has cooled to room temperature, remove the internal parts and clean the plastic residue from the outer wall of the cement ring 12 and the inner wall of the confining seat 14.

[0110] S204. Insert the drain plug 9 and small sealing ring 8 into the threaded hole at the lower end of the female threaded connector 7 in their original positions. Fill the internal parts with clean water. Insert the injection line 1, injection connector 2, and sealing cone ring 3 into the threaded hole at the upper end of the male threaded connector 4 in their original positions.

[0111] S205. Then place the internal components into the confining pressure vessel 14. The injection pump injects clean water into the internal components through the injection pipeline 1 to pressurize them. The pressure is transmitted to the cement ring 12 through the casing thread gap, increasing the pressure until the cement ring 12 ruptures, simulating the rupture of the cement ring outside the downhole casing.

[0112] S3. Thread plugging performance test

[0113] Inject the sleeve thread sealant to be evaluated into the inner cavity of the inner component until the sleeve thread sealant returns from the crack of the cement ring 12. At this time, remove the inner component, remove the drainage module, and release the sleeve thread sealant. The sleeve thread sealant at the thread mating surfaces of the two joints remains stationary.

[0114] Inject the dissolving agent into the cavity of the internal component to flush away any remaining plugging agent from the bushing threads;

[0115] Remove the drainage module installed at the bottom of the female connector 7 and remove the injection module;

[0116] Then place the internal components into the pressure vessel seat 14;

[0117] Place the confining pressure vessel cover 16 onto the confining pressure vessel base 14 and screw it on. Install the injection module inside the confining pressure vessel cover 16.

[0118] The entire device is placed in a water bath and heated, and pressure is applied to the entire internal components. The temperature and pressure are kept constant and stabilized according to the downhole temperature and pressure to simulate the downhole conditions when the plugging agent in the crack of the casing thread and cement sheath is cured. After the plugging agent in the casing thread is completely cured, the heating is stopped, the pump pressure is released, and after the temperature drops to room temperature, the injection module is removed.

[0119] Remove the entire apparatus from the water bath and remove the pressure vessel cover 16.

[0120] The injection module is installed inside the male connector 4, and pressure is applied to the inner cavity of the internal component through the injection module;

[0121] The sealant that has hardened inside the bushing thread is pressure tested to test the pressure-bearing capacity of the bushing thread sealant and the results are recorded.

[0122] Replace the male thread connector 4, female thread connector 7, and plastic diaphragm 13, and change the axial screw depth of the two connector threads to set different radial thread clearances, thereby simulating different leakage rates of the bushing threads. Repeat the above steps to test the sealing effect of the bushing thread plugging agent under different leakage rates.

[0123] Specifically as follows:

[0124] S301. Inject the casing thread plugging agent to be evaluated into the internal components through injection line 1 until the plugging agent returns from the crack in the cement sheath 12, and stop injecting the plugging agent to simulate the squeezing pressure and discharge rate of the downhole casing thread and cement sheath leakage.

[0125] S302. Remove the internal parts, remove the drain plug 9, and release the plugging agent in the device. The residual plugging agent at the root of the female thread 11 is discharged from the threaded hole below the female thread connector 7 through the drainage funnel 10. Due to the small clearance of the sleeve thread and the high viscosity of the plugging agent, the plugging agent on the threaded surfaces of the male thread 5 and the female thread 6 of the sleeve remains stationary.

[0126] S303. Inject the dissolving agent through the injection line 1 to flush away the residual dissolving agent in the injection line 1, and discharge the waste liquid from the threaded hole below the female connector 7;

[0127] S304. Insert the drain plug 9 and the small sealing ring 8 into the lower end of the female threaded connector 7 in their original positions, tighten the drain plug 9, and ensure that the small sealing ring 8 forms sufficient sealing force on the female threaded connector 7 and the drain plug 9. Remove the injection connector 2, the sealing cone ring 3 and the injection pipeline 1.

[0128] S305. Place the internal components into the confining pressure vessel base 14, connect the confining pressure vessel cover 16 with the large sealing ring 15 to the confining pressure vessel base 14, and install the injection connector 2, sealing cone ring 3 and injection pipeline 1 into the threaded hole at the upper end of the confining pressure vessel cover 16.

[0129] S306. The entire device is placed in a water bath for heating. At the same time, the injection pump pressurizes the internal components through the injection pipeline 1. The device is kept warm and pressure is stabilized according to the downhole temperature and pressure to simulate the downhole conditions when the casing thread gap and the plugging agent in the cement sheath 12 crack solidify.

[0130] S307. After the plugging agent inside the sleeve thread has completely cured, stop heating, release the pressure of injection line 1, and after the system temperature drops to room temperature, remove the injection connector 2, sealing cone ring 3 and injection line 1 from the confining pressure vessel cover 16, remove the entire device from the water bath, and remove the confining pressure vessel cover 16.

[0131] S308. Place the internal components into the confining pressure vessel seat 14, and then connect the injection connector 2, sealing cone ring 3 and injection line 1 to the threaded hole at the upper end of the male thread connector 4 in their original positions. Inject clean water into the internal components through the injection line 1 to test the pressure resistance of the sealant that has hardened in the sleeve threads and cement ring cracks.

[0132] S310. Replace a set of male thread connector 4, female thread connector 7 and plastic diaphragm 13, and change the axial screw-in depth of the male thread 5 and female thread 6 of the casing to set different radial thread clearances, thereby simulating different leakage rates of the casing threads. Repeat the above steps to test the sealing effect of the plugging agent to be evaluated under different leakage rates of the casing threads.

[0133] This invention, by simulating downhole temperature, pressure, and thread leakage rate conditions, can intuitively reflect the leakage of downhole casing threads and cement sheaths, as well as the sealing effect of plugging agents. It fills the technical gap in the simulation test of casing thread plugging agent sealing performance and avoids the blindness of casing thread plugging construction.

[0134] Those skilled in the art will understand that the above embodiments are specific examples of implementing the present invention, and in practical applications, various changes in form and detail may be made without departing from the spirit and scope of the present invention.

Claims

1. A casing thread leak-off simulation device, characterized by: It comprises a male threaded joint (4) and a female threaded joint (7) arranged in up and down and screwed with each other, the screwed structure is a columnar body with closed ends and hollow cavity, an injection module is detachably and sealingly installed at the top closed end of the columnar body, a drainage module is detachably and sealingly installed at the bottom closed end of the columnar body; The simulation liquid is injected into the columnar body from the injection module, and is drained from the screwed thread of the columnar body and / or drained from the drainage module; It further comprises a surrounding pressure vessel seat (14) and a cement ring (12) concentrically sleeved from outside to inside, the columnar body screwed by the two joints is seated in the cement ring (12), the top end surface of the cement ring (12) is located at the waist of the male threaded joint (4) and is higher than the top end surface of the female threaded joint (7); A plastic diaphragm (13) melted by heat is further arranged between the surrounding pressure vessel seat (14) and the cement ring (12), the plastic diaphragm (13) is a cylindrical body with closed bottom and open top, and the top end surface of the plastic diaphragm (13) is higher than the top end surface of the cement ring (12); The surrounding pressure vessel seat (14) is a cylindrical body with closed bottom and open top, the surrounding pressure vessel cover (16) is sealingly screwed at the open top end, and the male threaded joint (4) and the female threaded joint (7) and the cement ring (12) are enclosed in the cavity formed by the surrounding pressure vessel seat (14) and the surrounding pressure vessel cover (16). An installation hole for screwing in the injection module is formed at the center of the surrounding pressure vessel cover (16). By adjusting the axial screwing depth of the threads of the male threaded joint (4) and the female threaded joint (7), the radial gap at the threaded matching surface is changed to simulate the casing thread leakage channels with different leakage rates.

2. The casing thread leak-off simulation device of claim 1, wherein: The male threaded joint (4) is a hollow cylindrical structure with closed top and open bottom, an installation hole for screwing in the injection module is formed at the center of the closed top end, the outer circumferential surface of the open bottom end has a conical external thread, and the conical external thread is a casing male thread (5).

3. The casing thread leak-off simulation device of claim 2, wherein: The female threaded joint (7) is a hollow cylindrical structure with open top and closed bottom, an installation hole for screwing in the drainage module is formed at the center of the closed bottom end, the inner circumferential surface of the open top end has a conical internal thread, and the conical internal thread is a casing female thread (6). The casing male thread (5) and the casing female thread (6) form a pair of tapered pipe threads.

4. The casing thread leak-off simulation device of claim 3, wherein: The bottom of the inner cavity of the female threaded joint (7) is a drainage funnel (10) in inverted conical shape, the center of the drainage funnel (10) is the installation hole for screwing in the drainage module, and the drainage module at least comprises a drainage plug (9) sealingly screwed in the installation hole, and a small sealing ring (8) sleeved on the drainage plug (9) is arranged at the joint between the drainage plug (9) and the female threaded joint (7).

5. The casing thread leak-off simulation device of claims 1 or 2, wherein: The injection module at least comprises an injection joint (2) sealingly screwed in the top installation hole of the male threaded joint (4) or the surrounding pressure vessel cover (16), further comprises an injection pipeline (1) penetrating through the injection joint (2) and extending into the inner cavity of the male threaded joint (4) or the surrounding pressure vessel cover (16), and a sealing cone ring (3) sleeved on the outer wall of the injection pipeline (1) is further arranged in the top installation hole of the male threaded joint (4) or the surrounding pressure vessel cover (16).

6. The casing thread leak-off simulation device of claim 5, wherein: The sealing cone ring (3) is a spindle-shaped structure made of plastic material, which is located directly below the injection joint (2) and generates a conical deformation to seal the injection pipeline (1) and the injection joint (2), the injection pipeline (1) and the pin joint (4) or the injection pipeline (1) and the confining autoclave cover (16) under the axial pressure of the injection joint (2).

7. A method of casing thread leak-off simulation testing, characterized by, It adopts the casing thread leakage plugging simulation device according to any one of claims 1-6, and the test method is as follows: S1. Constructing a leakage channel Screw the injection module into the pin joint (4), and screw the drainage module into the box joint (7); Assemble the pin joint (4) and the box joint (7) to form an internal component; adjust the threads of the upper and lower joints to leave a radial gap at the threads, thereby forming a leakage channel; Pump clean water into the columnar body through the injection module, and the clean water returns from the screwed threads of the columnar body; Set a pump pressure value according to the driving pressure of the casing thread leakage test on site, adjust the axial screwing depth of the threads and the pump pressure, until the clean water return rate reaches the preset value, and record the clean water return rate corresponding to different axial screwing depths at the set pump pressure; S2. Simulating a broken cement sheath downhole Put the plastic diaphragm (13) into the confining autoclave seat (14); Remove the injection module and the drainage module; Put the assembled pin joint (4) and box joint (7) into the plastic diaphragm (13); Fill the casing cementing cement into the annular space between the plastic diaphragm (13) and the two joints to form a cement sheath (12); After the cement sheath (12) is solidified, remove the plastic diaphragm (13); Remove the pin joint (4) and the box joint (7), and install the injection module and the drainage module to form an internal component; Fill the internal cavity of the internal component with clean water; Put the internal component into the confining autoclave seat (14); Apply pressure to the internal cavity of the internal component, and continuously increase the pressure until the cement sheath (12) is broken; Simulate a broken cement sheath outside the casing downhole S3. Test the sealing property of the casing thread plugging agent Inject the casing thread plugging agent to be evaluated into the internal cavity of the internal component until the casing thread plugging agent returns from the cracks of the cement sheath (12), at which time the internal component is removed, the drainage module is removed, and the casing thread plugging agent is discharged, and the casing thread plugging agent at the threaded joint surface of the two joints remains stationary; Inject the plugging agent dissolving solution into the internal cavity of the internal component to flush the residual casing thread plugging agent; Install the drainage module at the bottom of the box joint (7) and remove the injection module; Put the internal component into the confining autoclave seat (14); Put the confining autoclave cover (16) on the confining autoclave seat (14) and screw it, and install the injection module in the confining autoclave cover (16); Put the entire device into a water bath and heat it, and apply pressure to the entire internal component, and according to the downhole temperature and downhole pressure, heat and stabilize the pressure to simulate the downhole conditions when the plugging agent in the casing thread and the cracks in the cement sheath is solidified, and stop heating after the plugging agent in the casing thread is completely solidified, remove the pump pressure, and after the temperature drops to room temperature, remove the injection module; Remove the entire device from the water bath and remove the confining autoclave cover (16). The injection module is installed in the pin connector (4), and pressure is applied to the inner cavity of the inner part by the injection module; The pressure test is performed on the solidified plug in the casing thread, the pressure-bearing capacity of the casing thread plug is tested, and the test results are recorded; A set of pin connector (4), box connector (7) and plastic diaphragm (13) are replaced, the axial screwing depth of the threaded connection of the two connectors is changed, so as to set different radial thread gaps, thereby simulating different casing thread leakage rates, and the above steps are repeated, so as to test the sealing effect of the casing thread plug to be evaluated under different leakage rates.

8. The casing thread leak-off simulation test method of claim 7 wherein, S2 simulates the rupture of the downhole cement sheath, fills casing cement into the annular space between the plastic diaphragm (13) and the two connectors to form a cement sheath (12), removes the plastic diaphragm (13) after the cement sheath (12) is solidified, and specifically as follows: The plastic diaphragm (13) and the annular space between the two connectors are filled with casing cement, and after the cement sheath (12) is solidified, if the inner part cannot be removed, the entire device is placed in a heating furnace to burn off the plastic diaphragm (13), and after the entire device cools to room temperature, the inner part is removed, and the plastic residue on the outer wall of the cement sheath (12) and the inner wall of the confining pressure pot seat (14) is removed.

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